As
the number of reported heart attacks, faintings and other medical emergencies
aboard airlines continues to soar, the government is considering changing the
way cabins are pressurized to provide more oxygen to passengers. The Federal Aviation
Administration and scientists across the industry are reevaluating a standard
that was set decades ago and based on studies of healthy servicemen in altitude
chambers. The modern airline cabin looks very different, as aging baby boomers
 many with health problems that can worsen suddenly and sometimes fatally
 fly farther and longer than ever before.

There is plenty of oxygen in the air inside airline cabins.
But because the barometric pressure is lower  equivalent to standing on
an 8,000-foot mountain  not as much oxygen reaches the bloodstream to be
carried to vital organs. Much of the focus on cabin air quality has been on the
spread of viruses such as the common cold. But a new focus is emerging as scientists
and doctors learn more about the threat that affects every airline passenger:
hypoxia, the term for too little oxygen.

This lack of
oxygen usually causes little more than a headache and a feeling of fatigue in
the average healthy flier. But passengers who have an underlying breathing, heart
or circulatory problem  even one they don't yet know exists  can suffer
serious medical emergencies when the oxygen level drops. Heart attacks are among
the more serious problems that hypoxia could cause during airline flights.

"People
are traveling to all ends of the Earth and very little attention has been given
to the impact and the insult on the human body during flight," says Marian B.
Sides, a vice president of the Aerospace Medical Association. As a military researcher,
she has studied the drop in oxygen levels at cruising altitudes.

"Ten
to 15 years ago, we were concerned about smoking on airlines. Now this is the
next level of concern," Sides says. "Going on an aircraft does in fact compromise
one's rate of oxygenation. The oxygen deficits are significant."

While
aviation experts reconsider  sometimes skeptically  the cabin pressure
standards, the National Academy of Sciences has appointed a panel of medical experts
to determine the exact health risks of breathing cabin air. The effort, which
is expected to be completed this year, comes as the number of reported medical
emergencies aboard airliners is increasing.

The FAA
does not track the number of medical emergencies in the air, but MedAire, a Phoenix-based
company that connects doctors with flight crews and ill passengers in flight,
says medical emergencies are at an all-time high. In the mid-1980s, there were
about 10 deaths each year on U.S. airliners.

Now, industry
officials estimate, as many as 100 people a year die because of medical problems
during flights. MedAire hears about many of them: The company helps 35 airlines
around the world and took 8,500 medical calls last year.

Aviation
experts say in-depth studies would be needed to determine if the hypoxia at cruise
altitude is to blame for the medical emergencies. But doctors atMedAire are
suspicious. They say that 21% of the calls they get are for passengers who pass
out. Heart and breathing problems accounted for 12% and 11%, respectively.

"The
issue of hypoxia is really significant for people with heart or lung disease,
and no one knows it," says Brent Blue, a doctor and pilot who sells oxygen-measuring
devices.

As
the plane soars, extremely hot air is drawn from the jet's engines, cooled and
piped into the cabin. This constant flow of very dry air keeps a life-sustaining
pressure in the cabin. But because the plane is designed to be as lightweight
as possible, it can only withstand so much pressure. The thin aluminum shell of
most jets expands like a balloon  as much as an inch  as the pressure
inside increases and the outside pressure decreases at high altitudes.

There
is just as much oxygen in the cabin air at cruising altitude as on the ground,
but because the atmospheric pressure is lower than at sea level, it is more difficult
for the body to absorb the vital gas. With less pressure, fewer oxygen molecules
cross the membranes in the lungs and reach the bloodstream.

The
result is a significant drop in the amount of oxygen in the blood  anywhere
from 5% to 20% depending on the person, the plane and the length of the flight.

With
less oxygen in the bloodstream, the vital organs soon get deprived.

The
reduced oxygen supply to the brain is why some suffer headaches while in flight,
one of the symptoms of hypoxia. When oxygen levels fall in the brain, the heart
tries to compensate by beating harder and faster. Another symptom of hypoxia is
fatigue.

But doctors say the body's efforts to compensate
can hurt people who fly with underlying medical conditions.

"Many
papers report that the rate of in-flight medical emergencies is higher in cases
with cardiovascular or cerebrovascular disorders," says Makoto Matsumura, of the
Heart Institute at Saitama Medical School in Japan, who presented new details
about the issue at last year's American Heart Association meeting. "The hypoxia
is related to the cabin environment. Therefore, it is important to draw attention
to the aged and the patients with hypertension who potentially have a vascular
disorder."

Joan Sullivan Garrett, who runs MedAire,
suspects that many of their medical emergencies are from passengers whose bodies
are already weakened by diseases struggling to compensate for a shortage of oxygen.

"In
a lot of these, the impetus is some sort of hypoxia," she says. "When you step
back and look at the average traveler, they are older and many have health problems
before they ever step on a plane."

Time for a new
standard?

Because the pressure in an airliner is
easy to control, the industry is considering whether it should change the minimum
pressure standards to try to prevent medical emergencies.

An
FAA rule requires pilots to keep jets pressurized to the level that is equivalent
to an 8,000-foot mountain or lower. The rule, FAA officials say, is based on altitude
chamber tests performed on healthy airmen decades ago.

But
the FAA says it does not monitor planes to see how they are pressurized while
carrying passengers.

One study performed by doctors
in the 1980s found pressurization differences across the fleet.

Each
plane must meet the same strict standard to go into service. But once it is in
use, everyday wear and tear can change the way the air flows in the cabin. Even
small dents in the floor by the door, where heavy carts are dragged aboard, can
make it more difficult to maintain cabin pressure.

The
more air the pilot takes from the engines to pressurize the cabin, however, the
more fuel it takes to fly. The air also reduces the engine's thrust.

"These
planes are flying up to 42,000 feet," says Stanley Mohler of Wright State University
School of Medicine in Dayton, Ohio, who has studied the health effects of flight.
"When you get up to that area, it takes a lot of fuel to keep the cabin pressurized."

As
engineers consider whether the atmosphere inside the cabin could be required to
be kept at pressurization equal to 6,000 feet, for instance, to increase passenger
oxygenation, the airlines want proof that a change is needed.

"The
airlines are going to resist," Mohler says. "If you lower the cabin pressure on
many of their airline flights, you're going to burn a lot more fuel."

The
aviation industry says that while it is worth studying, there is not yet any proof
that changing the pressure will help passengers.

"You
have to have some evidence that it's going to be salutary to the passengers,"
says Russell Rayman of the Aerospace Medical Association.

He
calls the FAA's 8,000-foot rule "rather arbitrary" and "a best guess," but he
says there is no proof that lowering it would help. "There is no evidence and
I think it will be very difficult to get it."

Some people
in the industry balk at the idea of changing the rules to meet the needs of people
with health problems.

"I feel sorry for somebody who
has vascular problems or breathing problems, but maybe they shouldn't be flying,"
says Dave Heekin, an airline captain. "If you are going to make it comfortable
for the most susceptible passengers you're going to have an airplane that you're
not going to be able to fly.

"I have compassion for
them but you can't do everything to the lowest common denominator."

Who's
responsible?

Heekin hopes his passengers begin
to take more responsibility for their health. "I'm tired of the flight attendants
telling me we have a passenger with breathing problems and we may have to land
in Omaha," Heekin says.

Garrett of MedAire says the
responsibility shouldn't rest with the airlines, which can't know their passengers'
medical baggage.

"I feel sorry for the airlines," she
says. "There is no way the airlines can possibly prepare to deal with the kinds
of problems and the critical nature of the problems travelers have today. How
can they be responsible? They don't know that my Aunt Agnes smokes."

Doctors
who have studied the problem agree.

They say two common
factors that cause hypoxia are often launched on the ground as passengers prepare
to board the plane.

When people drink too much alcohol,
the body does not use oxygen as efficiently, leading to what is known as histotoxic
hypoxia. And cigarette smoke damages the fragile membranes in the lung where oxygen
is exchanged.

People who have smoked for years and who
smoke several cigarettes before a flight can suffer what is known as hypemic hypoxia
before they board the plane.

Flight attendants say they
keep an eye on the "runners" who drink and smoke in the airport bar until the
last moments of boarding, then run to catch the plane before it leaves the gate.

"When
they get on board they decompensate," says Garrett, who was a flight nurse before
starting MedAire. "They get chest pain and in some cases they will have a cardiac
arrest."

Blue, a Jackson Hole, Wyo., physician and pilot,
says alcohol is a major reason for so many medical emergencies in flight.

"Alcohol
should not be served on an airplane," he says. "I can't think of anything worse
you could do on an airplane than drink."

Blue has a
Web site  Aeromedix.com  with information about hypoxia in flight.
And he sells fingertip devices that measure oxygen level in the blood. He began
selling to pilots so they could monitor themselves while flying their private
planes. But he says thousands of airline travelers have bought the devices, which
cost $380, in recent years.

If a healthy passenger suffers
any ill effects from hypoxia, it may be anything from a headache to tingling lips
to weakness or other annoyances. "But if they have a bad cold or upper respiratory
infection, walking pneumonia, coronary artery disease, emphysema, a lot of those
things, they'll notice it," Blue says. "Especially with coronary artery disease
they will be at significant risk."

He says the airlines
should not be "let off the hook" because they do not give any warning to their
passengers today about hypoxia or cabin pressurization.

"They
can say this flight will be 8,000 feet or 7,500 feet," he says. "Then you could
make a choice."

Rayman, a physician on the National
Academy of Sciences committee on cabin air quality, offers this perspective: "People
with coronary artery disease are flying every day. The great majority reach their
destination none the worse. Those with advanced or significant coronary artery
disease are at increased risk and should accordingly consult their physicians
before planning to travel by air."